As computing devices have increased in capabilities and features, demand for data storage devices has grown. Data storage devices have been used, for example, to store program instructions (i.e., code) that may be executed by processors. Data storage devices have also been used to store other types of data, including audio, image, and/or text information, for example. Recently, systems with data storage devices capable of storing substantial data content (e.g., songs, music videos, etc. . . . ) have become widely available in portable devices.
Such portable devices include data storage devices that have small form factors and are capable of operating from portable power sources, such as batteries. Some data storage devices in portable devices may provide non-volatile memory that is capable of retaining data when disconnected from the power source. Portable devices have used various non-volatile data storage devices, such as hard disc drives, EEPROM (electrically erasable programmable read only memory), and flash memory.
Flash memory has become a widely used type of semiconductor memory. Flash memory may provide a non-volatile memory in portable electronic devices and consumer applications, for example.
Two types of flash memory are NOR flash and NAND flash. In general, NOR flash may differ from NAND flash in certain respects. For example, NOR flash typically provides the capacity to execute code in place, and is randomly accessible (i.e., like a RAM). For example, NOR flash may provide code storage and direct execution in portable electronics devices, cell phones, and PDAs.
In comparison, NAND flash can typically erase data more quickly, access data in bursts (e.g., 512 byte chunks), and may provide more lifetime erase cycles than comparable NOR flash. NAND flash may generally provide non-volatile storage at a low cost per bit as a high-density file storage medium for consumer devices, such as digital cameras and MP3 players, for example. NAND flash may also be used for applications such as data storage in camera cell phones.
In some data storage systems, memory accesses may be interleaved across multiple memory locations. In RAID-0 type systems, for example, data are split up into N blocks that are written to or read from N memory locations at the same time. Instead of having to wait on the system to write 8 k to one memory location, an interleaved system can simultaneously write blocks of 2 k to each of four different memory locations.